A beam line ion implanter generates a well defined ion beam and directs the ion beam at a target surface of a substrate. The ion beam may strike the target surface of the substrate at any incident angle of the ion beam relative to the target surface to implant energetic ions of the ion beam into the substrate. A desired incident angle may be specified before an implant and any deviation from the desired incident angle can significantly impact the results of the implant.
An angle misalignment between the target surface of the substrate and the incident ion beam may be caused by several mechanisms and may lead to deviation from the desired incident angle. For example, the angle misalignment may be caused by a variation of the actual path of the incident ion beam from a desired path and/or a variation of the actual position of the substrate from a desired position of the substrate. Hence, it is desirable to determine any angle misalignment during an alignment check procedure before an implant. If there is an angle misalignment, the substrate may then be re-positioned relative to the incident ion beam to compensate for any angle misalignment. Measurement and correction of any angle misalignment is crucial to ensure accurate and repeatable angle performance of the implanter.
One method of determining angle misalignment between the incident ion beam and the target surface of the substrate requires a plurality of substrates during an alignment check procedure. Each of the plurality substrates is positioned at a different known offset angle by positioning the substrate relative to the ion beam and the entirety of each substrate is then implanted with ions from the incident ion beam. In a typical implementation of this procedure, nine separate substrates are implanted at nine different incident angles. Angle sensitive data from each substrate is then measured and the average value of the angle sensitive data from each is used to determine the angle misalignment. The angle misalignment may then be accounted for with an offset in the home position of the substrate.
This conventional method suffers from several drawbacks. First, material and processing costs increase with each substrate utilized. Second, it is difficult to ensure that each of the plurality of substrates has a similar surface orientation. This can then lead to inconsistency when measuring angle sensitive data from different substrates with slightly different surface orientations. Third, this method takes time that can adversely affect machine availability of the beam line ion implanter due to increased downtime. Fourth, variations in a substrate positioning apparatus may result in variations in substrate positioning for each substrate further degrading the quality of the results.
In semiconductor device manufacturing, the substrates may be cut from a crystalline semiconducting material that is grown into a cylindrical ingot. The substrates may therefore have a disk shape and may also be referred to as a wafer. These substrates may be sliced to obtain a desired crystalline plane at the target surface of the substrate and polished to ensure a flat target surface. However, the resulting target surface of the substrate may be formed from a miscut of the cylindrical ingot relative to the desired crystalline plane. This may sometimes be referred to in the art as “substrate miscut”. A conventional ion implanter assumes that there is either no substrate miscut or that the substrate miscut stays the same for all substrates to be processed in the implanter, and this assumption may lead to angle misalignment of the substrate relative to the incident ion beam. The substrate miscut may vary depending on the particular source of the particular substrate and how it was sliced relative to the desired crystalline plane.
Accordingly, there is a need for an improved method to determine an angle misalignment between a target surface of a substrate and an incident ion beam in beam line ion implanters. There is also a need for a method to determine any crystal miscut in the substrate.